1. Technical Field
The present invention relates to a method of forming a fine pattern, and particularly, to a method of forming a fine pattern employing self-aligned double patterning.
2. Discussion of the Related Art
As the integration density of semiconductor devices increases, technology for integrating many devices in a narrow area is required. In order to integrate a plurality of devices in a narrow area, it is required to reduce the size of a device formed on a semiconductor substrate.
The high integration of a semiconductor is closely related to a photolithography process in processes of fabricating the semiconductor device. Specifically, the minimum size of a pattern formed through the photolithography process is determined by limiting resolution of an exposure apparatus. The resolution of such an exposure apparatus is determined depending on the wavelength of a light source. That is, as the wavelength of the light source is shorter, the resolution of the exposure apparatus is more increased. Accordingly, a light source having a short wavelength has been continuously developed to increase the resolution. For example, a photo process has been developed by sequentially using a G-line laser having a wavelength of 436 nm, a I-line laser having a wavelength of 365 nm, a KrF laser having a wavelength of 248 nm, an ArF laser having a wavelength of 193 nm and an F2 laser having a wavelength of 157 nm as light sources. In addition, a process of using an X-ray or electron beam as a light source has been developed. As such, it is necessary to develop a light source in accordance with the short wavelength of the light source and develop a photoresist corresponding to the light source. However, a great deal of development cost is required in the development of a new light source and a photoresist corresponding to the light source.
Therefore, studies and research have been conducted to provide methods of forming fine patterns having a narrower width than the limiting resolution of an exposure apparatus used in a conventional process by using the exposure apparatus as it is. A method of forming the fine pattern has been disclosed in U.S. Pat. No. 5,686,223, entitled “Method for reduced pitch lithography” by Cleeves. According to Cleeves, a photolithography process is performed twice to form first and second photoresist patterns. Specifically, first photoresist patterns are formed on a substrate by performing a first photolithography process. After stabilizing the first photoresist patterns, second photoresist patterns are formed between the first photoresist patterns on the substrate. As such, the photoresist patterns formed through the two photolithography processes have a reduced pitch. However, as the integration density of semiconductor devices becomes higher, a pitch is more reduced. As a result, when forming the second photoresist pattern formed through the second photolithography process, the second photoresist patterns may not be precisely formed at a desired position due to misalignment.